The present invention relates generally to control systems used with single engine aircraft, and more particularly to a back-up control system which inactivates a faulty primary control system and maintains controllable flight sustaining thrust with event of control system failures.
The F101 aircraft engine employs a hydromechanical main engine control to provide, at pilot demand, automatic control of core engine functions essential for non-augmented thrust management. All other control features which are not categorized as essential for delivery of minimum acceptable flight sustaining thrust are electronically controlled.
When failure modes develop within the computational section of the hydromechanical main engine control, and its companion pressure and temperature sensors, they can result in the inability of the engine to deliver flight sustaining thrust. It is desirable, particularly in single engine aircraft application, to provide a back-up control system which will allow inactivation of a faulty primary system and engagement of a secondary system which will provide means of delivering controllable flight sustaining thrust.
The task of providing a back-up control system for single engine aircraft is alleviated, to some extent, by the systems of the following U.S. patents, the disclosures of which are incorporated herein by reference:
U.S. Pat. No. 3,764,095 issued to Schenbeck;
U.S. Pat. No. 3,905,241 issued to Downing et al;
U.S. Pat. No. 4,245,315 issued to Barman et al;
U.S. Pat. No. 4,489,904 issued to Soederberg;
U.S. Pat. No. 4,137,707 issued to Wanger; and
U.S. Pat. No. 4,248,040 issued to Kast.
Barman et al disclose an ignition limp home circuit for electronic engine control systems. Various functions of an internal combustion engine are controlled using a programmed microprocessor, which receives information concerning one or more engine-operating parameters such as: manifold absolute pressure, throttle position, engine coolant temperature, air temperature, engine speed, and the like. The limp home circuit permits the engine to function for a predetermined time even after the microprocessor fails, to enable the vehicle to get to a place of repair.
Downing et al disclose an electric flight control system including three or more flight command signal transmission channels. A discriminator prevents a malfunction of any one channel from causing the mechanical output signal to malfunction.
Soederberg shows a mechanism for actuating an auxiliary power source in an aircraft. This source takes the form of a ram-air turbine. Schenbeck shows a multichannel autopilot for aircraft in which the channels are independent so that, if one channel becomes inoperative, the system can still continue to achieve an automatic landing.
Kast and Wanger both disclose an integrated control system for a gas turbine engine. Wanger combines a primary electronic control system with a hydromechanical back-up control system.
While the prior art systems are exemplary, the F101 aircraft engine, as well as its derivatives, have been observed to manifest four specific indications which indicate the failure of the main engine control system. These specific indications are: (a) the power lever is at a position requesting a level of dry thrust which is at or above a predetermined threshold; (b) core engine speed is below that required to deliver the predetermined level of dry thrust; (c) core engine speed is not increasing; and (d) turbine temperature is beneath the allowable limit.
From the foregoing discussion, it is apparent that there currently exists the need for a back-up control system which supports the F101 aircraft engine and its family of derivative engines. The present invention is intended to satisfy that need.